Ammonia, carbide synthesis

The high capital cost, about 1500/kW, is the principal deterrent to growth of the IGCC concept. The abiUty to remove up to 99% of the sulfur species from the combustion products make the IGCC an environmentally desirable option as make calcium carbide (see Carbides), from which acetjiene is made. Synthesis gas for methanol and ammonia production is also made from gasification of coke. 

Subsequent studies have failed to support the carbide theory, and it is now generally accepted that carbides of the type proposed by Craxford play little or no part in the Fischer-Tropsch synthesis (86, 87). It has, however, recently been suggested, by analogy with the mechanism proposed for the Haber synthesis of ammonia, that carbides formed by dissociative absorption of carbon monoxide would be expected to be readily hydrogenated and could therefore be of importance in Fischer-Tropsch synthesis over heterogeneous catalyst (88). 

TVA Process (Refs 85, 93 102). In 1933 the Tennessee Valley Authority inherited a World War I plant designed to produce ammonia by a roundabout and obsolete method in the following steps first the manuf of lime and subsequently f a carbide, then Ca cyan amide, ammonia, nitric acid and finally AN. In 1940 a modern high-pressure ammonia plant was constructed, in which there were used an improved ammonia synthesis cataiysr and a water-gas conversion catalyst. During WW II, the TVA produced... 

Table 14.2 Synthesis of carbides and nitrides by reaction of a (bcc) metal film with CH4/H2 (10% methane) or with pure ammonia in a furnace... 

A common precursor to LnN are the simple inorganic amides Ln(NH2)x (x = 2, 3) which can be placed between the nitrides and the alkyl substituted amides. Their main use lies in the synthesis of other solid materials like lanthanide hydroxides [21,33], carbides [34] or above-mentioned nitrides. Very recently solutions of europium and ytterbium in liquid ammonia have been rediscovered as synthetic tools (Sect. 7.1). 

Shultz, Seligman, Shaw, and Anderson (5) attempted to prepare nitrides by treating raw (oxide) iron catalysts directly with ammonia. An analogous reaction, the formation of iron carbides by treatment of raw precipitated catalysts with carbon monoxide or synthesis gas, can be carried out at temperatures between 200° and 325°C. However, ammonia treatment of a precipitated catalyst (Fe203-Cu0-K2C03, Bureau of Mines number P3003.24) at 300°, 350°, and 400°C. resulted... 

Generation of a bernyne intermediate. A general principle of synthesis devised by Bunnett involves creation of an intermediate benzyne having a nucleophilic center so located that it can add intramolecularly to the triple bond. An example is the synthesis of 3-acetyloxindole from o-chloroacetoacetanilide (Union Carbide Chem. Co.) with potassium amide in liquid ammonia. In another synthesis o- and m-halo isomers gave the same product. 

Table VII presents the estimated investments. The methanol case investment reflects the same gasifier type as used for the IBG and SNG cases. A conceptual Chem Systems methanol synthesis step is used. EPRI is sponsoring the development of the Chem Systems technology (5 ). The ammonia case investment reflects the same wood gasification concepts, employs pressure swing adsorption for hydrogen gas purification (based on information provided by the Linde Division, Union Carbide Corporation), and uses a conventional high-pressure ammonia synthesis loop.

In 1898 Frank and Caro in Germany developed the cyanamide route, in which very high temperatures were used to fix elemental nitrogen to obtain calcium cyanamide from calcium carbide (Eq. 11.4). Hydrolysis of calcium cyanamide then produced ammonia and calcium carbonate (Eq. 11.5). For many years the cyanamide produced predominantly went into ammonia synthesis. 

In the case of the ammonia synthesis, iron nitrides instead of carbides were identified. in spent catalysts (Fe4N, Fe3N, and Fe2N). 

Pnictides LnQ (Q = Group 15 element) having the NaCl structure are made by direct synthesis, with other routes for the nitrides including the reaction of the lanthanide hydride with either nitrogen or ammonia like the carbides, they are readily hydrolyzed to the hydride QH3. 

Kummer et al. prepared the necessary carbided catalysts most of the studies were conducted with a promoted, fused, synthetic ammonia type catalyst containing 2.26 percent AI2O3, 0.62 percent Si02, and 0.21 percent Zr02 as promoters. CO chemisorption indicated that 35 percent of the catalyst surface was iron and 65 percent was promoter. Synthesis was affected at temperatures from 240 to 300 °C, 1 atm pressure and, in most cases, CO/H2 =1/1. Calculations for the fraction of the reaction via iron carbide as a... 

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